As mentioned in a comment on LOGBACK-910, the AsyncAppender will silently drop events when the current thread is interrupted. The simplest test for this is:

Thread.currentThread().interrupt();
log.warn("message 1"); // This was always dropped
log.warn("message 2"); // This is also dropped since LOGBACK-910 was fixed

Instead I expect the calls to block until the messages can be added to the queue and the interrupt status to be unchanged.